Single room occupancy (more commonly abbreviated to SRO) is a form of housing that is typically aimed at residents with low or minimal incomes who rent small, furnished single rooms with a bed, chair, and sometimes a small desk. SRO units are rented out as permanent residence and/or primary residence to individuals, within a multi-tenant building where tenants share a kitchen, toilets or bathrooms. SRO units range from 7 to 13 square metres (80 to 140 sq ft). In some instances, contemporary units may have a small refrigerator, microwave, or sink.

SROs are a form of affordable housing, in some cases for formerly or otherwise homeless individuals. SRO units are the least expensive form of non-subsidized rental housing, with median rents even in New York City ranging from $450 to $705 per month in 2013. The term is primarily used in Canada and US. Since the 1970s and 1980s, there has been an increasing displacement of SRO units aimed at low-income earners in a process of gentrification, with SRO facilities being sold and turned into condominiums. Between 1955 and 2013, almost one million SRO units were eliminated in the US due to regulation, conversion or demolition.

The term SRO refers to the fact that the tenant rents a single room, as opposed to a full flat (apartment). While roommates informally sharing an apartment may also have a bedroom and share a bathroom and kitchen, an SRO tenant leases the SRO unit individually. SRO units may be provided in a rooming house, apartment building, or in illegal conversions of private homes into many small SRO rooms. There is a variety of levels of quality, ranging from a "cubicle with a wire mesh ceiling", at the lowest end, to small hotel rooms or small studio apartments without bathrooms, at the higher end. They may also be referred to as "SRO hotels", which acknowledges that many of the buildings are old hotels that are in a poor state of repair and maintenance. The acronym SRO has also been stated to mean "single resident only". The terms "residential hotel" or "efficiency unit" are also used to refer to some SROs.